Variable geometry for controlling the flow of air to a combustor

ABSTRACT

The outer liner of an annular combustion chamber for a gas turbine engine is constructed of a rigid cylinder having a plurality of air inlet holes downstream of the primary combustion zone. The amount and the velocity of the air admitted through the air inlet holes to the combustor is controlled as a function of temperature by a construction which varies the geometry of the combustor adjacent the holes. The variable geometry consists of a frustro-conical sleeve mounted coaxially with the outer liner. One end of the sleeve is welded to the outer liner upstream of the air inlet holes. The other end extends downstream past the holes and provides an air inlet gap. A corrugated ring is mounted in the gap on the free end of the sleeve. As the hot gases pass over the sleeve, it expands closing the gap to a minimum determined by the depth of the corrugations of the strip.

United States Patent [1 1 Melconian VARIABLE GEOMETRY FOR CONTROLLING THE FLOW OF AIR TO A COMBUSTOR Jerry O. Melconian, Stratford, Conn.

[52] US. Cl. 60/3923, 60/3929, 60/3965 [51] Int. Cl. F02c 9/14 [58] Field of Search "60139.23, 39.29,

[56] References Cited UNITED STATES PATENTS 2,837,893 6/1958 Schirmer 60/3923 2,770,096 11/1956 Fox 60/3923 UX 3,362,470 1/1968 Richardson.... 60/3965 X 2,884,759 5/1959 Sevcik 60/3965 3,589,128 6/1971 Sweet 60/3965 2,684,573 7/1954 Marskell 60/3923 51 July 17, 1973 Primary Examiner-Clarence R. Gordon AttorneyCharles M. Hogan and Irwin P. Garfinkle [57] ABSTRACT Theouter liner of an annular combustion chamber for a gas turbine engine is constructed of a rigid cylinder having a plurality of air inlet holes downstream of the primary combustion zone. The amount and the velocity of the air admitted through the air inlet holes to the combustor is controlled asa function of temperature by a construction which varies the geometry of the combustor adjacent the holes. The variable geometry consists of a frustro-conical sleeve mounted coaxially with the outer liner. One end of the sleeve is welded to the outer liner upstream of the air inlet holes. The other end extends downstream past the holes and provides an air inlet gap. A corrugated ring is mounted in the gap on the free end of the sleeve. As the hot gases pass over the sleeve, it expands closing the gap to a minimum determined by the depth of the corrugations of the strip.

13 Claims, 3 Drawing Figures PATENTEU 7'975 3. 745,766

IN VENTOR.

JERRY O. MELCONIAN VARIABLE GEOMETRY FOR CONTROLLING THE FLOW OF AIR TO A COMBUSTOR BACKGROUND OF THE INVENTION Until recently most combustor designs have been based on good cold starting performance without consideration of exhaust emissions at maximum power condition. However, recent changes in the law regarding pollution of the environment require that combustors be designed so that minimum exhaust emissions result. v

From a technical point of view the requirement for good cold starts and low exhaust emissions are diametrically opposite. A good cold start requires a fuel rich in primary combustion zone whereas minimum exhaust emissions at maximum power require a fuel lean primary combustion zone. These opposing requirements suggest the need for variable geometry. The present invention provides a variable geometry combustor which changes the cooling air inlet area as a function of temperature, thereby varying the percentage of air that enters the primary combustion zone as a function of temperature.

THE DRAWINGS DESCRIPTION OF THE INVENTION Referring to the drawings, an annular reverse flow combustor is shown positioned within the casing 12 of a gas turbine engine. The space 14 between the combustor 10 and the casing 12 provides a path for compressed air exiting from the compressor and the diffuser (not illustrated) and supplied to the primary combustion zone of the combustor through a conventional swirler 16. Fuel is also supplied conventionally through a plurality of annularly spaced nozzles 18 (only one is shown). The combustor 10 is comprised of an inner annular liner 20 and a coaxial outer liner 22.

The outer liner 22 is provided with a plurality of stations of circumferentially spaced cooling air inlet holes 24a-d. While four stations are shown, it will be understood that any number may be used, depending only on the overall engine requirements. Coaxial with the air inlet holes at each station are annular elongated sleeves 26a-d, each peripherally welded to the inner circumference of the outer cylinder liner 22 upstream of the respective air inlet holes. The sleeves 26a-d extend rearwardly past the respective air inlet holes and at an acute angle. with respect thereto. Axially corrugated strips 28a-d are mounted within the air inlet gap between the liner 22 and the sleeves 26a-d. These strips are fixedly mounted on the free end of the respective sleeves. I

Under cold starting conditions the gaps between the sleeves 2642-11 and the liner 22 are a maximum, as depicted. However, as the combustor heats up, the sleeves 26a-d are subjected to more heat than the liner 22 and the relative expansion of the sleeves causes a reduction in the size of the gap between the sleeves and the liner wall. The size of the gap is limited to a minimum determined by the depth of the corrugations of the strips 28a-d.

The manner in which the disclosed construction functions is determined by the size of the air inlet holes 22. If the air inlet holes are very large and therefore do not serve to meter the amount of air flow into the combustor, then the quantity of air entering the combustor is a function of the variable geometry resulting from the expansion of the sleeves 26a-d. This means that under cold starting conditions a maximum amount of air is bypassed away from the main combustor zone and through the air inlet holes 24ad and through the gap between the sleeves and the liner wall 22. This causes a fuel rich mixture at starting. Under hot operating conditions, however, the gap between the sleeves and the cylinder is reduced to a minimum, and therefore a minimum amount of air is bypassed producing a fuel lean mixture in the primary combustion zone. This results in better engine performance both in cold starting temperatures and the hot operating temperatures.

If the holes 24a-d are sized so as to limit the amount of airflow into the combustor, i.e., if the holes 24a-d are metering holes, then the quantity of airflow remains relatively constant but the variable geometry results in an increase of the velocity of the airflow and an improvement in cooling efficiency.

. I claim:

1. In a variable geometry combustor comprising:

a liner forming a combustion chamber;

air inlet openings in said liner for admitting air to said chamber; and

temperature responsive means for controlling the flow of air through said openings, said means including a flexible member in said chamber, said member being expandable as a function of temperature, said member being secured at one end to said liner, the other end of said member being free, said free end of said member being positioned over said air inlet openings but spaced therefrom, the space between said free end and said liner being variable as a function of temperature when said member is subjected to heat.

2. The invention as defined in claim 1, and means for limiting the minimum size of said space.

3. The invention as defined in claim 2 wherein said means for limiting the minimum size of said space comprises a corrugated strip mounted within said space.

4. The invention as defined in claim 3 wherein said corrugated strip is secured to said free end of said member.

5. The invention as defined in claim 1 wherein said .lineris annular and wherein said member is a frustoconical sleeve secured to said liner within said chamber.

6. The invention as defined in claim 5, and means for limiting the minimum space between said free end and said liner.

7. The invention as defined in claim 6 wherein said means for limiting said minimum space is an annular strip having axial corrugations, said strip being mounted within said space.

8. The invention as defined in claim 7 wherein said strip is secured to said free end.

9. In a combustion chamber having a primary combustion zone and a dilution zone downstream from said primary combustion zone, the combination comprising:

an annular liner forming said combustion chamber;

air inlet openings in said liner downstream ofsaid pri- 10. The invention as defined in claim 9, and means mary combustion zone for admitting air to said for limiting the minimum space between said sleeve chamber at said dilution zone; and said liner.

an annular sleeve within said chamber, said sleeve 11. The invention as defined in claim 10 wherein said being expandable in response to variations in temmeans for limiting the minimum size of said space comperature, the periphery of one end of said sleeve prises an annular strip having axially extending corrubeing fixed to said liner upstream of said air inlet gations mounted within said space. openings, the other end of said liner being spaced 12. The invention as defined in claim 11 wherein said from said liner and extending downstream beyond annular strip is secured to said free end of said member. said air inlet openings, the space between said free 13. The invention as defined in claim 12 wherein said end and said liner being variable as a function of sleeve is frustro-conical.

temperature when said sleeve is subjected to heat. 

1. In a variable geometry combustor comprising: a liner forming a combustion chamber; air inlet openings in said liner for admitting air to said chamber; and temperature responsive means for controlling the flow of air through said openings, said means including a flexible member in said chamber, said member being expandable as a function of temperature, said member being secured at one end to said liner, the other end of said member being free, said free end of said member being positioned over said air inlet openings but spaced therefrom, the space between said free end and said liner being variable as a function of temperature when said member is subjected to heat.
 2. The invention as defined in claim 1, and means for limiting the minimum size of said space.
 3. The invention as defined in claim 2 wherein said means for limiting the minimum size of said space comprises a corrugated strip mounted within said space.
 4. The invention as defined in claim 3 wherein said corrugated strip is secured to said free end of said member.
 5. The invention as defined in claim 1 wherein said liner is annular and wherein said member is a frusto-conical sleeve secured to said liner within said chamber.
 6. The invention as defined in claim 5, and means for limiting the minimum space between said free end and said liner.
 7. The invention as defined in claim 6 wherein said means for limiting said minimum space is an annular strip having axial corrugations, said strip being mounted within said space.
 8. The invention as defined in claim 7 wherein said strip is secured to said free end.
 9. In a combustion chamber having a primary combustion zone and a dilution zone downstream from said primary combustion zone, the combination comprising: an annular liner forming said combustion chamber; air inlet openings in said liner downstream of said primary combustion zone for admitting air to said chamber at said dilution zone; an annular sleeve within said chamber, said sleeve being expandable in response to variations in temperature, the periphery Of one end of said sleeve being fixed to said liner upstream of said air inlet openings, the other end of said liner being spaced from said liner and extending downstream beyond said air inlet openings, the space between said free end and said liner being variable as a function of temperature when said sleeve is subjected to heat.
 10. The invention as defined in claim 9, and means for limiting the minimum space between said sleeve and said liner.
 11. The invention as defined in claim 10 wherein said means for limiting the minimum size of said space comprises an annular strip having axially extending corrugations mounted within said space.
 12. The invention as defined in claim 11 wherein said annular strip is secured to said free end of said member.
 13. The invention as defined in claim 12 wherein said sleeve is frustro-conical. 